1. Field of the Invention
The present invention relates generally to methods and systems for removing contaminant matter from natural and man-made porous materials including, for example, cement, asphalt, tile, granite, marble, and other stone materials. The present invention also relates to polymer materials that may be used in conjunction with such methods and systems to remove contaminant matter from such materials.
2. State of the Art
Natural and man-made porous materials and structures employing such materials may become contaminated with contaminant matter, such as radionuclides of uranium, plutonium, americium, californium, radium, iridium, cesium, strontium, and cobalt (as well as other fission products of such radionuclides), due to radioactive waste disposal and storage activities, unintentional leakage of radioactive waste, and fallout from atmospheric releases of radioactive material. For example, cement or asphalt roadways may be contaminated with radionuclides due to unintentional spills that occur during transportation of radioactive waste material from a waste generation site to a waste storage site. As another example, surfaces of buildings, monuments, bridges or other man-made structures that are formed from or are surfaced with porous materials, such as brick, cement, granite, marble, and other stone materials, could be contaminated with radionuclides upon the detonation of a “dirty” bomb (a bomb that includes radioactive material) such as might be detonated in an urban setting.
In events such as those described above, the contaminated structures and exposed surfaces of materials of such structures may need to be decontaminated before persons are allowed within the vicinity of the contaminated area and prior to resuming use of contaminated structures and proximity to surfaces thereof. When contaminated structures include porous materials (such as, for example, cement, asphalt, granite, marble, and other stone materials), at least some of the contaminant radionuclides may be deposited within pores, cracks, vugs and/or voids that extend into the porous materials from the exterior surfaces thereof. Contaminant radionuclides deposited within such pores, cracks, and/or voids may be relatively difficult to remove from the porous material, thereby complicating the decontamination process for such structures.
Furthermore, when contaminant radionuclides are deposited on a structure that includes a porous material, the radionuclides may become more tightly bound to the porous material with the passage of time, as the radionuclides migrate deeper within the pores, cracks, vugs and/or voids of the porous material and form surface complexes with the substrate materials surrounding such pores, cracks, and/or voids. Therefore, it may be necessary or desirable to remove radionuclides from contaminated structures and materials as soon as possible after a contaminating event. However, access to contaminated areas by decontamination personnel may be delayed for a period of time after such a contaminating event. For example, access to contaminated areas by decontamination personnel may be delayed until after emergency response personnel have evacuated and secured the contaminated area, and identified the nature and extent of the contamination. Such delays of access to contaminated areas by decontamination personnel may exacerbate the problem associated with the increasing difficulty of removing radionuclides from porous materials and structures with the passage of time.
One method for removing radionuclides from porous materials is described in U.S. Pat. No. 5,421,906 to Borah. The method involves applying a precleaning aqueous fluid to a contaminated surface, rinsing the precleaning fluid from the surface with water or a solution of water and sodium citrate, applying an aqueous extraction fluid to the contaminated surface, and washing the extraction fluid from the surface. The precleaning aqueous fluid comprises from about 4 to about 10 wt. % sulfamic acid, from about 5 to about 10 wt. % hydrofluoric ammonium bifluoride, from about 2 to about 4 wt. % hydrochloric acid, about 1 to about 4 wt. % surfactant, about 6 to about 12 wt. % sodium citrate, about 2 to about 5 wt. % oxalic acid, about 10 to about 20 wt. % triethanolamine; and, optionally, about 1 to about 2 wt. % d-limonine. The aqueous extraction fluid comprises about 5 to about 8 wt. % surfactant, about 4 to about 8 wt. % of an emulsifier containing quaternary amines, isopropyl alcohol and glycerine, about 15 to about 20 wt. % ethylene diamine tetracetic acid, about 5 to about 10 wt. % ethylene glycol monobutyl ether, about 4 to about 8 wt. % of a chemical pH buffer agent, about 4 to about 8 wt. % triethanolamine, and about 4 to about 10 wt. % of a composition selected from the group consisting of ethylene-bis(oxyethylenenitrilo)-tetracetic acid, 1,2 diamino-cyclohexane-tetracetic acid, hydroxyethylene diamine tetracetic acid, nitrilotriacetic acid and sodium gluconate.
Another method for removing radionuclides from porous materials is described in U.S. Pat. No. 5,763,734 to Nachtman et al. The method involves applying polyurea elastomers, other isocyanate plural component systems, polyurethanes, polyamides, latex, or mixtures thereof, at a temperature of at least about 100° F., to a contaminated substrate, and then removing the applied material to remove contaminants from the substrate.